Molten carbonate fuel cells utilize hydrogen and/or other fuels to generate electricity. The hydrogen may be provided by reforming methane or other reformable fuels in a steam reformer that is upstream of the fuel cell or within the fuel cell. Reformable fuels can encompass hydrocarbonaceous materials that can be reacted with steam and/or oxygen at elevated temperature and/or pressure to produce a gaseous product that comprises hydrogen. Alternatively or additionally, fuel can be reformed in the anode cell in a molten carbonate fuel cell, which can be operated to create conditions that are suitable for reforming fuels in the anode. Alternately or additionally, the reforming can occur both externally and internally to the fuel cell.
An article in the Journal of Fuel Cell Science and Technology (G. Manzolini et. al., J. Fuel Cell Sci. and Tech., Vol. 9, February 2012) describes a power generation system that combines a combustion power generator with molten carbonate fuel cells. Various arrangements of fuel cells and operating parameters are described. The combustion output from the combustion generator is used in part as the input for the cathode of the fuel cell. One goal of the simulations in the Manzolini article is to use the MCFC to separate CO2 from the power generator's exhaust. The simulation described in the Manzolini article establishes a maximum outlet temperature of 660° C. and notes that the inlet temperature must be sufficiently cooler to account for the temperature increase across the fuel cell. The electrical efficiency (i.e. electricity generated/fuel input) for the MCFC fuel cell in a base model case is 50%. The electrical efficiency in a test model case, which is optimized for CO2 sequestration, is also 50%.
An article by Desideri et al. (Intl. J. of Hydrogen Energy, Vol. 37, 2012) describes a method for modeling the performance of a power generation system using a fuel cell for CO2 separation. Recirculation of anode exhaust to the anode inlet and the cathode exhaust to the cathode inlet are used to improve the performance of the fuel cell. The model parameters describe an MCFC electrical efficiency of 50.3%.
In a natural gas combined cycle power plant, exhaust gas from the gas turbine can be passed to a heat recovery steam generator (HRSG). A HRSG can include an inlet for receiving the exhaust gas from the turbine and an outlet that exhausts the exhaust gas received from the turbine after heat energy has been extracted from the exhaust gas. Between the inlet and outlet is a flow path, in which multiple heat exchangers are located. The heat exchangers extract heat from the exhaust gas as the gas travels from the inlet to the outlet. Different types of HRSGs can include different types and number of heat exchangers that generate steam for use in a steam turbine or elsewhere for process heat. For example, a three stage HRSG can include three different heat exchangers each generating either high, intermediate, or low pressure steam.